Fixation of a ceramic structural member by way of gliding component in a femoral part

ABSTRACT

The invention relates to a knee-joint endoprosthesis with a metallic femoral part ( 2 ) anchored in the femur that articulates with a tibial part anchored in the tibia bone, the articulating surface of the femoral part ( 2 ) being a ceramic structural member ( 3 ) that is connected to the femoral part ( 2 ) in mechanically stable manner. With a view to optimising the attachment of the ceramic structural member ( 3 ) to the femoral part ( 2 ), various possible solutions are proposed.

[0001] This is a divisional application of U.S. Ser. No. 09/774,716,filed Feb. 1, 2001, which is a continuation of application Ser. No.09/008,427, filed Jan. 16, 1998 (now U.S. Pat. No. 6,214,051).

BACKGROUND OF THE INVENTION

[0002] The invention relates to a knee-joint endoprosthesis.

[0003] Known from WO 95/23567 is a knee-joint endoprosthesis having ametallic femoral part anchored in the femur that articulates with atibial part made of polyethylene which is anchored in the tibia bone.The articulating surface of the femoral part is formed by a ceramicstructural member that is connected to the femoral part in mechanicallystable manner.

SUMMARY OF THE INVENTION

[0004] The object underlying the invention is to improve a knee-jointendoprosthesis in such a way that the attachment of the ceramicstructural member to the femoral part is optimised.

[0005] In one embodiment according to the invention the ceramicstructural member is anchored on the femoral part by means of a conicalclamping device. To this end a conical slot is expediently produced inthe femoral part, into which slot the conical lateral surfaces of thestructural member are inserted. The angle of the conical clamping devicepreferably amounts to between 5° and 20°. The larger the angle, the moreeasily the structural members can be removed during a further operation,even after an implantation.

[0006] In a preferred embodiment the conical clamping device is disposedonly in the region above what is the loading tone the knee is extended.

[0007] In another preferred embodiment the conical clamping deviceextends over the entire region of the articulating surface.

[0008] In an alternative embodiment the structural member is anchored onthe femoral part by means of at least one fixing screw. A conicalclamping device would be dispensed with in this case.

[0009] Use is preferably made of two structural members perendoprosthesis. However, use may also be made of only one structuralmember, which then has two articulating surfaces.

[0010] In another alternative embodiment the ceramic structural memberis connected to the femoral part in non-detachable manner by shrinking,soldering or welding. Soldering also includes active soldering.

[0011] This attachment can be improved if the ceramic structural memberis additionally connected to the femoral part by means of a congruentsurface arrangement. The latter may be constituted by, for example,interlocking slots and ribs. In an advantageous configuration, theceramic structural member is additionally connected to the femoral partby means of a slot/spring connection. The latter is particularlyexpedient when there is shrinking on. When there is a slot/springconnection, a rib on the structural member, for example, projects into aslot in the femoral part, or vice versa. However, many variants of thecongruent surface arrangement are possible.

[0012] In another alternative embodiment the ceramic structural memberis in the form of a layer and is secured or applied by vapourdeposition, spray application or such like. The structural member isaccordingly a layer in this case. Of course, this layer may also consistof several individual layers. A ceramic material for the layer or theother structural members would be, for example, aluminum oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Further features of the invention will emerge from the figureswhich are described below. Illustrated are:

[0014]FIG. 1 is a cross-section through a femoral part with a structuralmember inserted with the aid of a conical clamping device taken alongline A-A of FIG. 1(c),

[0015]FIG. 1b is the same section as in FIG. 1a, but rotated through180°, taken along line B-B of FIG. 1(c),

[0016]FIG. 2 is a lateral section through a femoral part with astructural member mounted with the aid of a conical clamping device, theconical clamping device being disposed only above the loading zone,

[0017]FIG. 3 shows the attachment of the structural member to thefemoral part with the aid of a fixing screw and

[0018]FIG. 4 shows the attachment of the structural member to thefemoral part by shrinking, FIG. 4a representing a section like FIG. 1band FIG. 4b representing a section like FIGS. 2, 3.

[0019]FIG. 5 shows the attachment of the structural member to thefemoral part by a slot/spring connection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In FIGS. 1a, 1 b and 1 c a metallic femoral part 2 is shown invarious sections. A slot 5 or two slots 5 are produced in the femoralpart 2 in the region of the articulating surface. At their sides theseslots 5 have conical surfaces with angles between 5° and 20°. Enclosedin the slots 5 are ceramic structural members 3 which have correspondingconical lateral surfaces, so that a conical clamping device 4 is formed.The structural members 3 are not shown articulating with a tibial partanchored in the tibia bone. In this embodiment the slot 5 extends alongthe entire articulating surface. However, several slots 5 or individualnotches may also be provided so that the structural member 3 is anchoredto the femoral part 2 only at individual points by means of a conicalclamping device 4.

[0021]FIG. 2 shows a lateral section through a femoral part 2 with,likewise, a structural member 3 that is mounted with the aid of aconical clamping device 4. The conical clamping device 4 in this case,as distinct from the embodiment of FIG. 1, is disposed only above whatis the loading zone when the knee is extended. To this end a clampingsurface that is not as large as that in FIG. 1 is produced in thefemoral part 2.

[0022]FIG. 3 shows the attachment of the ceramic structural member 3 tothe femoral part 2 by means of a fixing screw 1. To this end a bore 7 isdisposed in the structural member 3 and a thread 6 is disposed in thefemoral part 2. The fixing screw 1 projects through the bore 7 into thethread 6 and in this way anchors the structural member 3 to the femoralpart 2.

[0023] If necessary, several fixing screws can also be used, which areadvantageously disposed sunk in the structural member 3.

[0024]FIG. 4 shows a femoral part 2 that has a slot 10 on its tibialside. The associated ceramic structural member 3 has a rib 11 that iscongruent with the slot. FIG. 4a shows the femoral part 2 incross-section and FIG. 4b shows it in longitudinal section. Thestructural member 3 is attached by shrinking it on. But it may also besoldered on or welded on. In this case the slot/spring connection mayoptionally be dispensed with.

[0025]FIG. 5 shows the attachment of the structural member 3 to thefemoral part 2 by a slot/spring connection (i.e., a rib on one of theceramic structural member 3 and the femoral part 2 and a slot in theother of the femoral part 2 and the ceramic structural member 3.

1. A method for forming a knee-joint endoprosthesis, comprising:providing a tibial part to be anchored in a tibia bone; providing ametallic femoral part to be anchored in the femur and articulate withthe tibial part; and soldering or welding an articulating surfacecomprising a ceramic structural member to said metallic femoral part. 2.A method for forming a knee-joint endoprosthesis, comprising: providinga tibial part to be anchored in a tibia bone; providing a metallicfemoral part to be anchored in the femur and articulate with the tibialpart; and vapour depositing or spraying an articulating surfacecomprising a ceramic structure member on said metallic femoral part.